Controlled engine exhaust gas recirculation (xe2x80x9cEGRxe2x80x9d) is a known technique for reducing oxides of nitrogen in products of combustion that are exhausted from an internal combustion engine to atmosphere. A known EGR system comprises an EGR valve that is controlled in accordance with engine operating conditions to regulate the amount of engine exhaust gas that is recirculated to the induction fuel-air flow entering the engine for combustion so as to limit the combustion temperature and hence reduce the formation of oxides of nitrogen.
It is known to mount an EGR valve on an engine manifold where the valve is subjected to a harsh operating environment that includes wide temperature extremes and vibrations. Stringent demands are imposed by governmental regulation of exhaust emissions that have created a need for improved control of such valves. Use of an electric actuator is one means for obtaining improved control, but in order to be commercially successful, such an actuator must be able to operate properly in such extreme environments for an extended period of usage. Moreover, in mass-production automotive vehicle applications, component cost-effectiveness and size may be significant considerations.
A known EGR valve typically relies on a valve that is actuated by a movement of a valve stem by an electromagnetic actuator. The EGR valve is typically mounted to a manifold or a housing that has one port exposed to exhaust gases and another port exposed to an intake manifold of the engine. Under certain operating conditions, the valve abuts a valve seat surface so as to prevent exhaust gases from flowing into the intake manifold. Depending on the operating conditions, the valve can be moved away from the seat to permit a controlled amount of exhaust gases into the intake manifold.
An EGR valve that possesses more accurate, quicker and generally linear response can be advantageous by providing improved control of tailpipe emissions, improved driveability, and/or improved fuel economy for a vehicle having an internal combustion engine that is equipped with an EGR system.
Further, a valve that is more compact in size while delivering the same or an increased magnitude of force over the travel of the valve stroke can be advantageous because of limitations on available space in a vehicle engine compartment. Thus, it would be advantageous to provide for an EGR valve that is compact yet powerful enough to deliver a generally constant force over an extended stroke distance.
In one preferred embodiment of the invention, an exhaust gas recirculation valve is provided. The exhaust gas recirculation valve includes a housing, a closure member, and an electrical actuator. The housing has a first port in fluid communication with a second port. The closure member is disposed in the housing in one position along a longitudinal axis to occlude fluid communication between the first port and the second port. The closure member is located in one of a plurality of positions that permits fluid communication between the first port and the second port. The closure member is coupled to an elongated member of the electrical actuator. The electrical actuator is coupled to the housing. The actuator includes an inner core, magnetic member, outer core, bushing, and bobbin assembly. The inner core has a first opening disposed about the longitudinal axis. The magnetic member is disposed adjacent the inner core. The magnetic member has a second opening disposed about the longitudinal axis. The outer core is generally coaxial with respect to the inner core. The outer core extends along the longitudinal axis and surrounds the inner core and the magnetic member so as to form a generally toroidal interior volume. The outer core includes a third opening disposed about the longitudinal axis. The bushing is coupled to the inner core, the magnetic member and the outer core along the longitudinal axis. The bushing supports an elongated member. The bobbin assembly is coupled to the elongated member and supports a coil, the coil being disposed in the generally toroidal interior volume so that the coil moves along the longitudinal axis upon energization of the coil.
In another preferred embodiment of the invention, an electrical actuator is provided. The electrical actuator includes a casing, inner core, outer core, magnetic member, bushing, and bobbin assembly. The casing has a first casing end spaced from a second end along a longitudinal axis. The inner core is disposed proximate the first casing end. The inner core has a first circumferential surface disposed about the longitudinal axis. The inner core includes a first opening disposed about the longitudinal axis. The magnetic member is located proximate to the inner core. The magnetic member has a second circumferential surface disposed about the longitudinal axis and circumferentially aligned with the first circumferential surface so as to provide a generally continuous surface. The magnetic member includes a second opening disposed about the longitudinal axis. The outer core is generally coaxial with respect to the inner core. The outer core extends along the longitudinal axis and surrounds the first and second circumferential surface so as to form a generally toroidal interior volume. The outer core includes a third opening disposed about the longitudinal axis. The bushing is coupled to the inner core, the magnetic member and the outer core along the longitudinal axis. The bushing supports and guides an elongated member for movement along the longitudinal axis. The bobbin assembly is coupled to the elongated member and supports a coil. The coil is disposed in the generally toroidal interior volume so that the coil moves through a portion of the interior volume along the longitudinal axis upon energization of the coil.
In yet another embodiment of the invention, an exhaust gas recirculation valve is provided. The exhaust gas recirculation valve includes a housing, electrical actuator, and a force balance closure assembly. The housing has a first port with a seat surface in fluid communication with a second port. The housing includes an annular chamber disposed about a longitudinal axis and surrounds a hub portion coaxial to the longitudinal axis. The first port is adapted to fluidly communicate with a port of an exhaust manifold of an engine, and the second port is adapted to fluidly communicate with a port of an intake manifold of the engine. The force balance closure assembly being disposed in the housing and includes a closure member, valve stem, head and annular seal. The closure member is disposed in one position along a longitudinal axis to occlude fluid communication between the first port and the second port. The closure member is movable to one of a plurality of positions permitting fluid communication therebetween the ports. The stem extends through the hub of the housing along the longitudinal axis so as to couple to the electrical actuator. The head is coupled to the stem. The head has a face portion and a body portion. The face portion includes a sealing surface contiguous to the seat surface of the first port in the one position. The face portion also includes a first face area spaced from a second face area along the longitudinal axis. The first face area is exposed to the first port. The second face area is exposed to the second port. At least one passage extends through the face portion. The body portion has a generally cylindrical body extending about the longitudinal axis from the face portion towards an end portion surrounding the hub and being surrounded by the annular chamber. The body portion forms an interior volume in fluid communication with the annular chamber and the passage. The annular seal is disposed in an annular groove of the end portion about the longitudinal axis. The annular seal has a circumferential surface contiguous to interior wall surface of the annular chamber so that the chamber is generally fluid tight with respect to the second port the end portion and the seal as the valve moves along the longitudinal axis in the chamber.
In yet another preferred embodiment of the invention, a method of operating an exhaust gas recirculation valve is provided. The exhaust gas recirculation valve has a housing, a closure member, and an electrical actuator. The housing includes a first port communicating with an exhaust port of the engine. The first port is in fluid communication with a second port. The closure member is disposed in the housing in a closed position along the longitudinal axis occluding fluid communication between the first port and the second port and one of a plurality of positions permitting fluid communication therebetween. The electrical actuator includes a first core, a magnetic member, a second core, and a bobbin assembly supporting a coil aligned along the longitudinal axis. The bobbin assembly is coupled to the closure member. The method can be achieved, in part, by maintaining the closure member in the closed position upon de-energization of the coil; and moving the bobbin assembly along the longitudinal axis in a volume radially outward of the magnetic member and one of the first and second cores when the coil is energized so as to move the closure member along the longitudinal axis.
In yet another preferred embodiment of the invention, a method of controlling an exhaust gas recirculation valve in an engine is provided. The valve has a housing that includes a first port that communicates with an exhaust port of the engine. The first port is in fluid communication with a second port. A closure member is disposed in the housing in a closed position along a longitudinal axis so as to occlude fluid communication between the first port and the second port, and in one of a plurality of positions that permits fluid communication therebetween. An electrical actuator has a first core, a magnetic member and a second core aligned along the longitudinal axis, and a bobbin assembly that supports a coil. The bobbin assembly is coupled to the closure member. The method can be achieved, in part, by maintaining the closure member in the closed position upon de-energizing the coil, and moving the bobbin assembly in a volume radially inward of one of the first and second cores and radially outward of the magnetic member and the other of the first and second cores along the longitudinal axis.
In yet another embodiment of the invention, a method of assembling a bobbin assembly to an electromagnetic actuator is provided. The electromagnetic actuator includes an outer core, magnetic member and inner core with a bobbin assembly. The electromagnetic actuator has an outer core surrounding both an inner core and a magnetic member about a longitudinal axis so as to provide a generally toroidal interior volume. The bobbin assembly has a generally cylindrical portion integral to a generally planar portion. The coil is mounted to the cylindrical portion. A bushing is coupled to the inner core, the magnetic member and the outer core along the longitudinal axis. The bushing supports and guides an elongated member. The method can be achieved, in part, by inserting a locating plate with a hub portion over the elongated member; and sandwiching the generally planar portion of the bobbin assembly to the locating plate with a retaining assembly along the longitudinal axis so that the bobbin assembly is aligned to the longitudinal axis relative to the outer core.